The ability to play is one of the principal criteria of mental health.

Montagu, Ashley. The Universal Nature of Play.

Bigotry and science can have no communication with each other, for science begins where bigotry and absolute certainty end. The scientist believes in proof without certainty, the bigot in certainty without proof. Let us never forget that tyranny most often springs from a fanatical faith in the absoluteness of one’s beliefs.

The second sentence is often misquoted as “Science has proof without any certainty. Creationists have certainty without any proof.” or “Religion gives us certainty without proof; science gives us proof without certainty.”